Public communication system comprising distributed stations, and station and sub-station for use in such a communication system

ABSTRACT

A public communication system for encrypted audio/video information has various selective entitlement organizations with respect to its distributed receiver station. Such receiver station comprises one or more receiver sub-stations for decrypting the received encrypted information by means of a decrypting key. Furthermore, the receiver station comprises one or more decription key sub-stations that may be interrogated by the receiver sub-stations and thereupon may verify a conditional access requirement, and in case of positive verification, forward decryption key information the interogating received sub-station. All said sub-stations are interconnected by a serial standard bus, so that the configuration of a station is flexible and may even be altered dynamically.

BACKGROUND OF THE INVENTION

The invention relates to a public communication system with distributedstations, comprising a broadcast sub-system for broadcasting encryptedaudio and/or video information, a governing accounting system fordistributing entitlements to the distributed stations and, in eachstation, a selectively activatable decryption sub-system which isverifiable by entitlement information in order to receive the encryptedinformation and to supply it to a reproduction apparatus afterdecryption. The foregoing may be realized as a system for paytelevision; payment can take place either by subscription or on thebasis of the actual use of the programs supplied. The entitlements canbe distributed in various ways, for example via a telephone link, incooperation with information from the encrypted audio/video signal ornot, by way of a system utilizing so-called chip cards, or by way of acoin box included in each station. It may be that access is granted togiven persons and not to other persons, without payment taking place. Inthat case a chip card is a very suitable identification means. Thebroadcast medium may be the ether or a cable link organization. Thesignal source may be a transmitter or a reproduction apparatus whichthen involves a cable link. The invention can be used notably forconsumer television but is not restricted thereto. It could as well beused for granting access to data bases which may be used by serial userstations simultaneously.

SUMMARY OF THE INVENTION

The system set forth operates simply if it involves only one accountingsystem which operates on a subscription basis. The inventor hasanticipated the increasing complexity which may arise when a pluralityof accounting systems operate in parallel, for example broadcastingsystems which are based in different countries; in that case theentitlements may be realized on respective different various bases andthe waveforms of the broadcast sub-system may be subject to differentstandards. It is inter alia an object of the invention to realize aneffective organization in a receiver station in such a communicationsystem in the event that the identity of the decryption sub-system isnot unambiguously known in advance because of said divergences, so thatvarious different decryption sub-systems could be represented in eachstation, thereby allowing as much flexibility in said representation, oralternatively, in the absence thereof in a particular station. Accordingto one of the aspects of the invention, the object is realized in thatthe invention provides a public communication system, comprising abroadcast sub-system for broadcasting encrypted audio and/or videoinformation, a plurality of distributed stations for decrypting of thisinformation after reception and for making decrypted informationavailable to a reproduction apparatus, and a governing accountingsystem/access control system for selectively making one or moredecryption keys available to each station, a station comprising at leastone decryption key sub-station (CASS) and at least one receiversub-station, all such sub-stations within each station beinginterconnected by means of a standard serial bus without a central buscontrol sub-station, each receiver sub-station comprising means forreceiving a current program selection from a user, storage means foridentifying a selective accounting system/access control system thereby,and accessing means for via said serial bus accessing a decryption keysub-station associated with said selective accounting system/accesscontrol system, for thereby verifying an entitlement, for uponverification deriving a decryption key therefrom, and for enabling afurther accessing operation in case of non-verification of saidentitlement. The standard bus allows any station to have an arbitraryset of receiver sub-stations and decryption key sub-stations, which maybe changed geometrically as far as the layout of the bus allows, andalso allows for adding and/or deleting any number of sub-stations.

The invention also relates to a station for use in such a system, andalso to a decryption key sub-station and a receiver sub-station for usein such a station. Various types of sub-stations may be easilyconnectable or disconnectable to the standard serial bus, which wouldalso allow to have an aggregate of sub-stations of various differentmanufacturers smoothly cooperate.

Further attractive aspects of the invention are recited in dependentclaims.

BRIEF DESCRIPTION OF THE FIGURES

The invention will be described in detail hereinafter with reference toseveral Figures.

FIG. 1 shows a communication system in accordance with the invention;

FIG. 2 shows a receiver sub-station for use in a station in accordancewith the invention;

FIG. 3 shows an decryption key sub-station for use in a station inaccordance with the invention.

SYSTEM DESCRIPTION

FIG. 1 shows a public communication system in accordance with theinvention. Block 20 represents a broadcasting sub-system which in thiscase feeds a parabolic antenna 22 for broadcasting audio and/or videoinformation in the form of programs. This information is encrypted bymeans of a predetermined encryption key. This key, or at least the keywhich is required for decryption, is not generally known. Theinformation reaches a satellite 24 in which it is amplified andretransmitted to a terrestrial parabolic antenna 26. Block 28 representsa demodulator/controller. This device amplifies the analog signals,performs FM demodulation, converts the demodulated signal into a bitstream and, controls the position of the antenna 26, if necessary, inresponse to signals on lines 31, 33 supplied respectively by receiversub-stations 30, 32 when position control of antenna 26 is utilized.This bit stream is applied to the receiver sub-stations 30, 32. Thereinthe information received is decrypted by means of a decryption key forsupply to reproduction apparatus 38, 40. Blocks 34, 36 representdecryption key sub-stations which make the decryption key available toreceiver sub-stations 30, 32, subject to conditions yet to be described.This is realized by communication via the serial bus 44. Such a serialbus is described per se in U.S. Pat. No. 4,429,384 and is known as a D²B bus; the invention, however, is not restricted to the use of this bus.A special advantage of the D² B bus consists in the absence of any buscontrol sub-station. This means that inter alia, access requests by theseveral sub-stations can be generated in mutual independence. Aparticular advantage of D² B is that the bus protocol allows for variousdifferent transmission bit rates. The electrical standardization of D² Ballows for many interconnected sub-systems that may be located atappreciable distances, such as would occur in a home or small officeenvironment. Block 42 represents a governing accounting system/accesscontrol system of the kind set forth. In the decryption key sub-stations34, 36 this system activates the decryption key associated with theencryption key used in the broadcasting sub-station. Activation in thesub-stations 34, 36 can be realized, for example via a telephone linkvia which key information is transmitted. Alternatively, thisinformation is already present and a selection is made between a numberof keys. It is also possible for a part of the key to be contained inthe program information so that it forms the actual decryption key inconjunction with information from the accounting system. The receiversub-stations 30, 32 comprise user activation inputs 46, 48 such as akeyboard or an infrared control element. Thus, a selection is possiblebetween "off" and "on" and possibly a program selection can be made by auser (station selection, channel selection and the like). The elements30, 32, 34, 36 and 38, 40 together constitute a station.

The system shown in FIG. 1 may also have a different construction; thenumber of accounting systems may be different (larger) and a pluralityof receiver sub-stations may be connected to the same antenna; on theother hand, each receiver station may also comprise its own decryptionkey sub-station.

The accounting system may be based on the chip card principle; this cardis introduced into the decryption key sub-station: the cards and thesub-station together contain sufficient information for decryption. Thechip card may be organized according to the debit principle: the card ispurchased by the consumer and represents a given value. Depending on theconsumption of given program information, this value is gradually usedup.

The audio/video signal (22, 24, 26) may also be fully or partly analog.In that case the analog signals are processed in thetransmitter/receiver; however, the value or code of the decryption keyis then stored in digital form in the decryption key sub-stations andcommunication takes place digitally. The transmission mechanism (22, 24,26) may also be based on a cable organization or a local reproductionapparatus. This does not constitute an essential difference. In additionto said sub-stations, further sub-stations may be connected to theserial bus. This does not introduce an essential difference either. Itmay be that given information is encrypted (the programs) while otherinformation is not (for example, commercials and program announcementsor summaries of the programs).

Furthermore, organizationally, a particular decryption key sub-stationmay be assigned to one or more receiver sub-stations. Also, a particularreceiver sub-station may have one or more decryption key sub-stationsassigned to it. Also, the physical topology (as distinct from thelogical topoloy) may be a single bus run, a plurality of runs thatconnect to a common junction, a closed loop-like run, or any otherconfiguration according to needs and electrical realizeablility.

CHARACTERISTICS OF A RECEIVER SUB-STATION

Characteristics of a preferred embodiment of a receiver sub-station willbe decribed in detail hereinafter, in combination with the previouslydescribed realization of a serial bus, i.e. the so-called D² B bus. Thebit formats, the composition of the messages, the changing-over betweenmodes at different bit rates, the organization at the level ofabsent/present acknowledge bits and the like will not be described forthe sake of brevity. The following data is present in the receiversub-station:

a. its own bus address; this is necessary because all bus messagescontain the own address of the broadcast sub-station;

b. the permissible standards of the audio/video information. Thisinformation defines the basic types such as those according to PAL,NTSC, MAC-family, MUSE and the like. These standards are known per seand will not be described herein. Generally speaking, the receiver willaccept one basic type at a given instant, but it is also possible tochange the basic type in the case of a change-over from one program toanother.

c. specific characteristic data concerning its own operation vis-a-vissaid serial bus, such as a facility for acting as a master station, theintended bit rate and other feasible bit rates, and the amount of bufferspace which is directly available for the storage of information.

d. the actually received or the basic type which can be directlyreceived for the AV (audio/video) signal;

e. possibly a presence table for the decryption key sub-stations whichare suitable for the respective basic types permissible in the receiversub-station as regards the audio/video signals. The relevant decryptionkey sub-stations, therefore, can be addressed by the receiversub-station concerned. Thus, for each decryption key sub-station such atable may contain:

a sequence number of the decryption key-sub-station in question

a sub-station address

basic type of the audio/video signal

type of the conditional access to the audio/video signal, such as at themoment, for example NRMSK, Eurocript-NTA/Philips, Eurocypher,Eurocrypt-CCETT/CanalPlus, Filmnet (analog); with the type there areassociated directly the encoding/encryption format, the key words,formulation/formating of the entitlement; the above types themselves aresubject to standardization;

possibly CAS-accounting system; this provides the name of the relevantorganization, such as "CanalPlus", "Scansat";

f. a table for storing the variables involved in the decryption process.In given cases a receiver sub-station is capable of performing aplurality of decryption processes simultaneously. Thus, for each type ofcode the table may contain:

a reference sequence number which can act so as to identify thedecryption process (together with the bus address of the decryption keysub-station) using in the relevant key word; this sequence number maytherefore, be included in the bus protocol;

a code which indicates which service or services as represented by theaudio/video signal can be offered by the relevant process;

a code which indicates whether the relevant service is free of charge,i.e. freely accessible, or whether decryption must be performed by meansof key information which is not available free of charge, and anindication of the decryption key or the whole decryption key or a partthereof, for use in the receiver sub-station;

a code which indicates that, even if the audio/video information isfreely accessible, a decryption operation must still be performed;

the number of the relevant decryption key sub-station.

CHARACTERISTICS OF A DECRYPTION KEY SUB-STATION

Characteristics of a decryption key sub-station will be described indetail hereinafter. Generally speaking, a decryption key sub-stationcontains information associated with a fixed decryption mechanism(possibly a number of such mechanisms). The key itself, and also anyaccounting information, may of course be variable, for example in that apositive financial balance is successively depleted. The stationaryinformation is the following:

the bus address of the serial bus in order to be addressable as a slavestation or as the own address when it acts as a master station, and alsomode information concerning the operation of the sub-station vis-a-visthe bus, such as the bit rate;

the basic type of the audio/video information, this is the signal orbroadcast standard (PAL, NTSC, etc.) whereto the conditional access,entitlements, keys and the like relate;

the signal standard; this is the standard (PAL, NTSC . . . etc.) wheretothe entitlements, keys and the like relate;

the type of conditional access for which the relevant decryption keysub-station is designed, for example the previously described set NRMSK,Eurocrypt-NTA/Philips, Eurocypher, Eurocrypt-CCETT/CanalPlus, etc. Infirst instance a single decryption key sub-station will act on a singletype of conditional access;

the name of the organization/agency which is the supplier of theinformation and/or distributes the entitlements in the system, forexample CanalPlus, etc.;

a unique customer number which is used, for example for bookkeepingpurposes.

A decryption key sub-station may be capable of performing variousprocesses within a given signal standard, for example in that the keyinformation is modified or chosen from a plurality of possibilitieswhich are present continuously. The entitlements can be processed inaccordance with predetermined specifications. For example, for eachprogram an hourly fee can be defined; this fee can be preset arbitrarilyfrom one program to another and/or from one organization to another.

APPLICATION PROTOCOL

An application protocol will be described hereinafter. Generallyspeaking, via the serial bus a dialog takes place between the receiversub-station and the decryption key sub-station. Instructions, requestsand acknowledgements or specifications can be communicated. Thespecifications may comprise zero, one, or more than one parameter.

The decryption key sub-station first makes itself known to all receiversub-stations in the station, for example when the mains voltage isswitched on. If this is accepted by a (the) receiver sub-station, it mayrequest the decryption key sub-station to supply all relevantinformation (i.e. the contents necessary for filling the table in thereceiver sub-station). When mains voltage is applied to a receiversub-station, it interrogates all decryption key sub-stations in thestation in order to fill its own table.

When a channel with conditional access is tuned to, the receiversub-station selects the signal package "0". This is standardized in saidsignal standard. When the relevant channel involves conditional accesswhich is applicable to the relevant service, this protection isactivated so that one or more relevant key words must be provided. Alldecryption sub-stations which are compatible with the relevant signalstandard and the conditional access involved, are then interrogated soas to determine whether they may provide any further key words. If thisis so, the decryption key sub-station concerned receives the parametersof the relevant service. The decryption key sub-station supplies the keyinformation to the receiver sub-station in the case of usability of thisservice. If applicable, the most ready decryption key sub-station isselected. The receiver station then receives the relevant key. When adecryption key sub-station does not have relevant key informationavailable when interrogated, its response is negative and, if possible,another decryption key sub-station is interrogated. When all decryptionkey sub-stations associated with the relevant standard give a negativeresponse, no entitlement can be verified, for example in that a givenperiod of time has expired or in that a positive account now has beenused up. In that case the receiver sub-station concerned detects thatall decryption key sub-stations have given a negative response andoutputs an error message in a suitable manner, for example a visualsignal on a LED, or a message from the reproduction apparatus. Thisaspect will not be described for the sake of brevity.

If information concerning entitlements is received via the audio/videochannel (i.e. via block 28 in FIG. 1), this information is are alsochecked first by means of the decryption key sub-stations which areloaded, if necessary, or the admission of a given group of customers isupdated. To this end, therefore, the decryption key sub-stations for therelevant signal standard and the type of conditional access must besearched for. It is again possible that the interrogated stations areabsent or already fully occupied, or alternatively, that the informationregarding the conditional access is not required. In case of anon-executable function met, a diversion is made either to a functionwhich can still be activated or, if this is also impossible, the systemsupplies an error message.

DESCRIPTION OF TWO SUB-STATIONS

FIG. 2 shows a receiver sub-station 74 for use in a station inaccordance with the invention. The information which has not yet beendecrypted arrives on input 50; in the present case this information isassumed to be digital information. Element 64 is a detector forspecific, non-encrypted codes which indicate the beginning and the endof a program, and also, for example for a code which identifies therelevant program (for example, in order to obtain commercialretrocoupling) and a statement of the fee which is to be paid out of apossible balance receivable in the decryption key sub-station. It may bethat the same code is periodically included in the program (for example,1× per second, possibly together with progressive updating of thepayments to be made; this signal arrives on input 68 of the businterface circuit cum control circuit 66. Furthermore, there is providedan input 49 for the reception of program selection signals, for examplea frequency channel. If necessary, these signals are processed so as toform a control signal on line 76 for block 28 in FIG. 1 (see the brokenlines 31, 33). The orientation of the parabolic antenna 26, thefrequency tuning, the modulation and the like can thus be readjusted.Alternatively, the signal on the line 49 is associatively processed sothat an optimum choice is pursued in block 28, for example the strongesttransmitter for a given channel identification. Under the control of thecode on the line 68 (which may generate an interrupt), the circuit 66checks whether the information indicated by the code corresponds to thedecryption procedures followed in the receiver sub-station. Initiallythis will not be the case and the presence table for the decryption keysub-stations will be consulted. The desired decryption key sub-stationis then activated, via the bus 72, in order to supply the keyinformation as has already been stated. The key information received isstored in a memory 62 which communicates directly with the specialdecryption device 60. This device receives the decrypted informationfrom the input 50 via a first-in first-out memory 52. In element 60decryption is performed in a known manner by means of a filter.Decryption operations are known per se; for brevity they will not bedescribed. After decryption the information words are stored in thefirst-in-first-out buffer 56 after which they are applied to therelevant reproduction apparatus via output 58. Arrow 54 indicates thatthe two first-in-first-out buffers are coupled; thus, the streams on thelines 50 and 58 are synchronous; the operation in the element 60 neednot be fully synchronized therewith. Block 66, or block 62, comprisesthe memory for storing said tables. The organization within the receiverstation is symbolically represented; the organization at the circuitlevel may be different. Depending on the required complexity, therespective functions can be performed by more complex or by simplercomponents. All internal communication can take place via a bus or viadedicated connections as shown.

FIG. 3 shows a decryption key sub-station for use in a station inaccordance with the invention. The sub-station 90 comprises an interfaceelement 82 to the serial bus 80 which also provides central control forthe sub-station. There is also provided a memory 84 which serves interalia for the storage of the described table information. There is alsoprovided an interface element 86 to a chip card 88 which can beintroduced into the decryption key sub-station in order to present theentitlement information. In this case the decryption key sub-station canact as a slave if the entitlements interrogation by the receiversub-station occurs sufficiently frequently. In other cases thedecryption key sub-station can also act as a master station, for examplefor indicating that the chip card has been introduced or removed, or forindicating that the decryption key sub-station has been activated ordeactivated in another manner.

I claim:
 1. A system for broadcasting encrypted information, comprisinga plurality of distributed stations for reception and decrypting of thisinformation and for making decrypted information available to areproduction apparatus, and a governing accounting system/access controlsystem for selectively making one or more decryption keys available toeach station, each station comprising at least one decryption keysub-station (CASS) and at least one receiver sub-station, all suchsub-stations within each station being interconnected by means of astandard serial bus without a central bus control sub-station, eachreceiver sub-station comprising means for receiving a current programselection from a user, storage means for identifying a selectiveaccounting system/access control system thereby, and accessing means forvia said serial bus accessing a decryption key sub-station associatedwith said selective accounting system/access control system, for therebyverifying an entitlement, for upon verification deriving a decryptionkey therefrom, and for enabling a further accessing operation in case ofnon-verification of said entitlement.
 2. In a system for broadcastingencrypted information among distributed stations, a station comprisingat least one receiver sub-station and at least one decryption keysub-station, all such sub-stations being interconnected by means of aserial bus without a central bus control sub-station, each receiversub-station comprising means for receiving a current program selectionfrom a user, storage means for storing a local bus address, a list ofaudio/video information standards to be received, and characteristicdata concerning the operation of the receiver sub-station vis-a-vis theserial bus, and means for identifying, by way of the program selectionreceived, an associated selective accounting system/access controlsystem, for then accessing an associated decryption key sub-station, forthereby verifying an entitlement, and for upon verification deriving adecryption key from said decryption key sub-station, and for enabling afurther accessing operation in case of non-verification of saidentitlement.
 3. In a system for broadcasting encrypted information amongdistributed stations, a station comprising at least one receiversub-station and at least one decryption key sub-station, all suchsub-stations being interconnected by means of a serial bus withdistributed bus control means, each receiver sub-station comprisingreceiving means for receiving a current program selection informationfrom a user, identification means for under control of said programselection information identifying an associated decryption keysub-station and thereupon accessing the latter sub-station via saidserial bus, the latter sub-station having verification means for undercontrol of said access verifying an entitlement information with respectto the program so selected, and forwarding means for under control of apositive verification forwarding means for under control of a positiveverification forwarding an entitlement information for the program soselected via said serial bus to the accessing receiver sub-station.
 4. Astation as claimed in claim 3, wherein said entitlement informationforwarded to said receiving sub-station comprises decryption keyinformation.
 5. A station as claimed in claim 2, 3 or 4, wherein saidserial bus is a D² B bus.
 6. A station as claimed in any of claims 2 to4, wherein each receiver sub-station further comprises means forreceiving encypted information inclusive of non-encrypted identificationinformation identifying a particular conditional access type as regardssaid encrypted information, detecting means for detecting saididentification information, bus interface means to a standard serial busfor under control of said detecting means putting an access request fora decryption key sub-station associated to said conditional decryptionkey sub-station receiving either decryption key information, oralternatively a refusal information.
 7. A station as claimed in any ofclaims 2 to 4, wherein said decryption key sub-station comprises meansfor storing an entitlement information, bidirectional bus interfacemeans to a distributed-control standard serial bus for receiving anentitlement interrogation signal and for transmitting an entitlementverification signal, and verification means for under control of saidentitlement interrogation signal, selectively in case of a verifiedentitlement, generating said entitlement verification signal onto saidserial bus.